Communication lines are commonly placed underground. As permitted, a narrow trench is dug along the intended path of the line and the line is laid in the trench and then covered. This procedure is not complex and relatively inexpensive. However, often it happens that an obstruction lays in the path and digging a trench is not permitted or is too difficult.
In such instances, the alternative is to drill a hole through the ground and under the obstruction. For example, if the lines are to be buried to a four foot depth, a partial trench is first dug to the four foot depth prior to the obstruction and a drill bit mounted on an extendable pipe is fed laterally along the desired path. The pipe is moderately flexible and, in at least one version, the pipe is turned by a powerful motor to turn the bit and thereby auger through the ground with the pipe being fed behind it. A flushing slurry is fed through the pipe and into and through to the leading end of the drill bit. Material that is loosened by the drill bit is flushed by the slurry back through the hole. The line is then pulled through the hole formed by the drill bit and pipe.
All of the above is common to the art of directional drilling. Not referred to, however, and also common to the process explained above, is the need to control the direction of drilling. The drill bit is designed so that it can be maneuvered to change direction. The drill bit itself has a digging head that is non-symmetrical, i.e., teeth are projected angularly from the axis of the drill bit on one side only. During normal drilling, the drill bit is rotated so that the digging action is symmetrically applied and the drill bit travels in a straight line. To change direction, the rotation is stopped and the drill bit is pushed through the ground. At whatever direction the teeth are projected, that is the direction that the drill bit will turn toward (up, down or to either side). When the desired new direction is achieved, the rotation of the bit is commenced to head the digging action in the new direction.
The location of the drill bit and the position of the teeth on the drill bit is monitored through the use of a known detection device. Thus, an operator may determine that the hole is headed too deep, too shallow or otherwise off line in one direction or the other. He stops the rotation of the drill bit with the teeth facing the desired direction. He then pushes the bit forward until the bit is properly directed (which may include a sequence of side to side oscillation of the drill bit) and the normal drilling action is continued.
Whereas existing drill bits work quite well in dirt, they do not work so well in rock or shale. A cone-type drill bit cutting head has been developed to improve performance in rock or shale. Rows of circularly arranged teeth are provided on a conical cutter head that is rotatably mounted about its conical axis to the end of a forwardly protruded and outwardly directed shank of the drill bit. The base portion of the cone side of the conical head carries one of the rows of teeth and with the mounting arrangement described is adjacent to the shank and extends laterally outwardly of the shank. The axis of the rotatable cone is directed inwardly and forwardly. The apex of the cone side and the teeth adjacent the apex cuts the material from the center of the hole while the teeth adjacent the base provide the laterally outermost cutting which forms the hole side.
Whereas the conical cutter is considered an improvement when directional drilling through rock and shale, it is not completely satisfactory (and sometimes unsatisfactory), and an objective of the present invention is to improve on the above-described cone-type drill bit.